Many people suffer from injury to the soft tissues of the wrist and carpal tunnel, often caused by frequent, sustained repetitive motion involving the hands. Repetitive activities which require the same or similar hand/wrist action can result in injuries which have been collectively referred to as Cumulative Repetitive Stress Syndrome or Repetitive Strain Injury. The most familiar and common of such wrist injuries is known as carpal tunnel syndrome which produces pain, discomfort, nerve conduction disturbances, and impairment of function of the hand and sometimes the arm as well. The most common symptoms of this condition include intermittent pain and numbness of the hand.
Carpal tunnel syndrome occurs when the median nerve which runs from the forearm into the hand, becomes pressed or squeezed at the wrist. The median nerve provides feeling in one's thumb and along with index, middle and ring ringers. The median nerve controls sensations to the palmar side of the thumb and these fingers as well as impulses to some muscles in the hand which allow the fingers and thumb to move. The median nerve receives blood, oxygen and nutrients through a microvascular system which is present in the connective tissue surrounding the nerve fiber. Increased pressure on the nerve fiber can constrict these microvessels and will reduce the blood flow to the median nerve. Any prolonged deprivation of oxygen and nutrients can result in severe nerve damage.
The median nerve passes through the carpal tunnel, a canal in the wrist surrounded by the carpal bones on three sides and a fibrous sheath called the transverse carpal ligament on the fourth side. In addition to the median nerve, the nine flexor tendons in the hand pass through this canal. When compressed, the median nerve will cause pain, weakness or numbness in the hand and wrist which may also radiate up along the arm. The median nerve can be compressed by a decrease in the size of the carpal canal itself or an increase in the size of its contents (i.e. such as the swelling of the flexor tendons and of the lubrication tissue surrounding these flexor tendons), or both. For example, conditions that irritate or inflame the tendons can cause them to swell. The thickening of irritated tendons or swelling of other tissue within the canal narrows the carpal canal, causing the median nerve to be compressed. The cross-sectional area of the tunnel also changes when the hand and wrist changes positions. Wrist flexion or extension can decrease the cross-sectional area, thus increasing the pressure exerted on the median nerve. Flexion also causes the flexor tendons to somewhat rearrange which can also compress the median nerve. For example, simple bending of the wrist at a 90 degree angle will decrease the size of the carpal canal. Without treatment, carpal tunnel syndrome can lead to chronic neural muscular disorders of the hand and sometimes the arm.
Treatment for carpal tunnel syndrome includes a variety of non-surgical as well as surgical procedures, wherein carpal tunnel release is one of the most common surgical procedures that is performed. Such surgery involves the severing of the transverse carpal ligament to relieve the pressure on the median nerve and is commonly performed via either open or endoscopic methods. In open methods, the skin lying over the carpal tunnel is incised after which the transverse carpal ligament is transected under direct vision. The skin is then reapproximated with sutures. Endoscopic methods require incision of the skin in one or more locations to allow for the insertion of an endoscope along with various tools that are needed to transect the ligament. Such tools typically include a combination of a specially configured scalpel and guide instrument. The insertion of such tools into proper position below, above or both below and above the target ligament further requires the formation of one or more pathways in the hand with attendant trauma to the surrounding tissue and the potential for nerve damage as well as a more protracted post-surgical healing process. Additionally, the use of a scalpel typically requires multiple passes thereof in order to complete a transection which causes a complex pattern of cuts to be imparted onto the severed ligament surfaces.
Less invasive techniques have been proposed including for example the use of flexible saw elements that are introduced into the hand and positioned adjacent to or wrapped about a portion of the target ligament after which the saw element is reciprocated to cut the tissue. A substantial disadvantage of a cut that is made by a saw-like instrument as opposed to a knife-like instrument is inherent in the fact that a kerf is created. The material that is removed from the kerf is either deposited in and around the surgical site or additional steps must be taken to retrieve such material. Additionally, the cut surfaces that are created by a saw tend to be relatively rough and abraded with microtrauma on the cutting surface that may increase inflammatory response (edema, erythema, heat and pain), could result in local tissue adhesions and scarring which can delay or complicate the healing process.
Alternatively, techniques have been proposed wherein a taut wire, string or filament is used to cut a ligament. The cut is achieved either by the tautening of the cutting element or alternatively, by reciprocating the taut element. Disadvantages associated with such an approach are inherent in the less than optimal geometry by which a taut wire can be brought to bear on the target ligament and by the invasiveness of the tightening apparatus.
A new method and apparatus is needed with which tissue such as a ligament can be percutaneously accessed and transected so as to cause a very minimal amount of disruption to the surrounding tissue and by which a smooth, kerf-less cut is achieved.